1. Field of the Invention
The present invention relates to a method for manufacturing a nitride semiconductor laser element, and more particularly relates to a method for manufacturing a cavity plane for a nitride semiconductor laser element.
2. Background Information
Cleavage, etching, and various other methods have been employed in the past to form a cavity plane for a nitride semiconductor laser element. Of these, forming a cavity plane by dry etching allows just the cavity plane part of the nitride semiconductor layer to be formed by etching, without etching all the way down to the lower part of the nitride semiconductor layer that makes up the laser element and the substrate on which this nitride semiconductor layer is laminated. Therefore, a plane protective film can be formed in wafer units, so the process is simplified, the advantage to which is lower cost, compared to a method in which the substrate and the nitride semiconductor layer formed on the substrate are split in the shape of a bar and a protective film for the cavity plane is formed in bar units to form a cavity plane by cleavage (see Japanese Laid-Open Patent Application H9-223844 and WO2002/103865).
However, when a cavity plane is formed by etching after a nitride semiconductor layer has been laminated on a substrate, a terrace-like horizontal face may be formed between the cavity plane and the element separation face after the element has been separated. This terrace-like horizontal face can block the light of the laser beam from the emitting plane part of the cavity plane, or reflect this light, etc., resulting in disturbance of the far field pattern.
Method that have been proposed to prevent this disturbance of the field image, and with which the formation of a terrace-like horizontal face is minimized, include a method in which a cavity plane is first formed, and then a V-shaped auxiliary groove is formed for substrate division (such as Japanese Laid-Open Patent Application H1-120885), a method in which a semiconductor layer is laminated on a substrate, an electrode is produced over an active layer, and then an element separation groove is formed, after which a cavity plane is produced by etching, and a method in which this element division groove is formed so that the angle formed between the groove face and the substrate face is an acute angle at an light emission-side plane (such as Japanese Laid-Open Patent Application 2000-106470).
However, with a method in which a V-shaped auxiliary groove is formed after the formation of the cavity plane, because the V-shaped auxiliary groove is V-shaped, the cavity plane has to be protected with a resist or other such protective film during this V groove formation. However, if the cavity plane is protected by covering it with a resist or the like, the thickness of this protective film will result that a distance will be opened up between the cavity plane and the auxiliary groove after etching due to the protective film becoming a mask, and this ends up being a problem in that a terrace-like horizontal face is formed between the cavity plane and the element separation face.
Even when the cavity plane is etched after the element separation groove has been formed, alignment of the cavity plane mask is necessary, and a terrace-like horizontal face is formed at the margin thereof.
Furthermore, when an element separation groove is formed by dicing or the like, a problem is that the nitride semiconductor layer is susceptible to damage.
When this element separation groove is formed such that the angle formed between the groove face and the substrate face is an acute angle, not only is it difficult to dice diagonally with good precision, but also it is difficult to form the grooves equidistantly spaced, so this approach is believed to be inefficient. Furthermore, with a completed element, since the substrate is removed from under the emission-side cavity plane, which is where heat is most likely to build up, another problem is that heat dissipation is worse.